How do I ask a user to enter a lone letter q to quit a program?

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I need to have the user to enter a line of characters into a program of which should keep running until the user enters a lone q to quit.

What I have tried:

C++

//mywhile.cpp -- entering q to quit
#include <iostream>
using namespace std;
int main()
{
    {int q{};
    cout << "Enter a line ('q' to quit): ";
    cin >> q;
    if (cin.fail())
    {
        cin.clear();
        cin.ignore('\n');
    }
    cout << "Try again: ";
    cin >> q;
    cout << "Thanks for entering: " << q << " . Goodbye. \n";
    }
    system("pause");
}

Here is what I have tried but it is not working so I don't know where my error is?

Posted 3-Nov-21 6:02am

Mountain town life

Updated 3-Nov-21 13:56pm

Rick York

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Richard MacCutchan 3-Nov-21 12:14pm

You accept input from the user but you never test to see exactly what letter they typed. Also the input variable should be a char variable for a single letter reply, or a std::string for a complete line. You have declared q as an array of integers which will not work for either case.

merano99 4-Nov-21 14:35pm

As you can see from our discussion below, there is no known C ++ solution to this frequently asked question. Under Windows there are solutions in C that also work under C ++.

3 solutions

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

merano99 · Answer 1 · 2021-11-03T13:04:00

Solution 2

The cheapest way on Windows would be this:

C++

#include <iostream>
#include <conio.h>

int main()
{
	char letter;

	std::cout << "enter 'q' to quit\n"; // ask user 

	do {
	letter = getch();
	} while (letter != 'q');
}

Posted 3-Nov-21 13:04pm

merano99

Comments

Richard MacCutchan 4-Nov-21 5:11am

The question is about C++, so why are you using getch rather than cin?

merano99 4-Nov-21 14:25pm

:-)
Out of desperation, because at this point it is neither platform-independent nor with "real" C ++.
If you don't like conio like me, I only see the possibility to use system calls directly. Unfortunately, it then becomes quite cumbersome. I also offered the solution here, see there.
I am not aware of any solution with cin that works without <enter>.

OriginalGriff · Answer 2 · 2021-11-03T06:58:00

Solution 1

As Richard says, you don't test your input.

Start here: 3 Ways to Compare Strings in C++ - JournalDev[^]

Posted 3-Nov-21 6:58am

OriginalGriff

Comments

merano99 3-Nov-21 18:03pm

The linked artikel is using <string.h>. It works, but <string> would be the first choice for C ++.

merano99 · Answer 3 · 2021-11-03T13:56:00

If you do not like the cheap version, here is a solution without conio.h for Windows

C++

#include <windows.h>
#include <strsafe.h>
#include <iostream>

int main()
{
	char letter;
	DWORD cNumRead;
	INPUT_RECORD irInBuf[128];

	std::cout << "enter 'q' to quit\n"; // ask user 

	do {
		HANDLE hStdin = GetStdHandle(STD_INPUT_HANDLE);
		if (hStdin == INVALID_HANDLE_VALUE) exit(1);
	
		// Enable the window input events (without mouse)
		if (!SetConsoleMode(hStdin, ENABLE_WINDOW_INPUT))
			exit(2);

		if (!ReadConsoleInput(hStdin, irInBuf, 128, &cNumRead)) {	
				DWORD dw = GetLastError();
				std::cout << "System Error: " << dw << "\n"				
				exit(3);
			}

		// Dispatch events 
		for (unsigned i = 0; i < cNumRead; i++) {
			switch (irInBuf[i].EventType)
			{
			case KEY_EVENT: // keyboard input
				if (irInBuf[i].Event.KeyEvent.bKeyDown) {
					letter = irInBuf[i].Event.KeyEvent.uChar.AsciiChar;
					std::cout << letter;
				}
				break;
			default:
				letter = ' ';
			}
		}

	} while (letter != 'q');
}

How do I ask a user to enter a lone letter q to quit a program?

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How do I ask a user to enter a lone letter q to quit a program?

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